top of page


This guide is all about composting, theres more info on loads of other ways of using your used growing mix, as well as how to reuse and recycle the rest of our products on the 'Resuse and Recycle' tab under 'More Info'.

Composting your Organic Growing Mix is a great way of saving money and resources - it can take as little as 4 weeks and means you can keep growing microgreens from the same soil many times, then, all you need to do is buy seeds.

If you want to re-use your soil or growing mix for growing microgreens then we recommend using this method:

Put it in a bucket. Take the contents of your trays (roots and soil) and put them in a bucket or any medium/large sized container (30L+), try and fill it as tightly as possible, you can do this by pushing down firmly on the contents.

Leave it for at least a month. Once it's full you can leave it inside or out, with a lid either loosely on or off completely, so at least a little bit of air can get in there, but no water can. Leave it for between 4-12 weeks.

Is it ready yet? The speed in which it composts depends on many factors, so the best thing to do, is rather than going off any set timescale, check and see if it's ready before using it. You will know it's ready, when it is a fine crumbly mix, without many seeds or lumps. If it's not ready, don't worry just come back later. It could be that it's too cold for, or it's not got the optimum moisture content, but it will get there eventually regardless.

Optional: Sterilisation... Sort of If your batch of growing mix for whatever reason showed many signs of mould during its original use, this is recommended. The reason you want to sterilise the soil is to reduce the chance of any mould forming (or flies spawning etc) when you use it to grow microgreens. There are a few ways to reduce the chance of mould and pests in your compost, the easiest way is by drying it out. You may well be able to grow more microgreens without any problems without doing this step so don't worry if you don't, but it's best practice to do so if you want to guarantee the best results. To dry it out fast, spread it over a surface, lie a tarp or a table outside on a dry (or even better dry and windy) day. Or if you're not in a rush, leave it next to a radiator indoors (or outdoors under cover if its warm outside), with the lid off, to allow air in, occasionally stirring or turning it to speed things up.

The next level above this, is to actually sterilise it in an oven, by heating it on a tray to over 70°C for 30 mins, which is possible for the keen amongst you, but in terms of effort, perhaps that compost that needs that level of treatment would be best of donated to your garden/to some friends with gardens and some fresh Organic Growing Mix ordered... just a thought!

Reuse it. You can use it just like you do with fresh Growing Mix, using your scoop, one part dry Growing Mix, one part water. If you're using a wet mix, simply add the desired amount to your tray.

The dream: 'The three bucket system'

Starting with three empty buckets. You fill up bucket no. 1 with used Growing Mix and set it aside to start composting.

One filling, one full and composting. Whilst bucket no. 1 is composting, you are filling up bucket no. 2 with used Growing Mix, until bucket no. 2 is full, then you set aside that too for composting, by that time, bucket no. 1 has composted, and it ready to be emptied.

One filling, one full and composting, one composted and emptying. Whilst bucket no. 2 is full and composting, you are emptying bucket no. 3, using the contents, to grow more microgreens, and putting the used Growing Mix created from those, into bucket no. 3, which will slowly fill as bucket no. 1 is emptied. By the time you have emptied bucket no. 1, bucket no. 3 will be full, and bucket no. 2 will be ready to be emptied.

And so it continues....

For example. A standard builders bucket is around 15L = 24 trays worth of compost. If you are on our Keen Grower subscription and growing 3 trays a week then it takes about 8 weeks to fill 1 bucket. Which should give plenty of time for the next bucket to be ready (fully composted) as soon as you are. And repeat...

Hope that helps you on your way to getting more out of your Organic Growing Mix!

bottom of page